Introduction: Superoxide dismutase (SOD) holds significant importance in the pharmaceutical, nutraceutical, and cosmeceutical industries due to its role in neutralizing toxic superoxide radicals. In this study, we investigated plant residues as a source of SOD enzyme.

Methods: Plant residues from five different plants were analyzed for their SOD enzyme content. Peels from watermelon (Citrullus vulgaris Schrad.), bitter orange (Citrus aurantium L.), three varieties of melon (Cucumis melo L.)—Hafidh Nafsah, Ananas, and Alasfer Alshtwi—banana (Musa paradisiaca L.), and potato (Solanum tuberosum L.) were evaluated. The extraction of each plant peel was performed using potassium phosphate buffer (50 mM KH₂PO₄, pH 7.8). Each sample was tested in triplicate for SOD activity and specific activity. Polyacrylamide gel electrophoresis (PAGE) was used to detect different SOD isoenzymes in the plant peels with and without the selective inhibitors potassium cyanide (KCN) and hydrogen peroxide (H₂O₂).

Results: Peels from melon, watermelon, and bitter orange exhibited higher SOD activity compared to peels from potato and banana. SOD activity remained stable for six months when stored in the freezer. Among the various local melon varieties studied, the Ananas variety exhibited the highest SOD activity and specific enzyme activity. Out of the different buffers tested for extracting the enzyme from melon peel, potassium phosphate buffer (50 mM KH₂PO₄, pH 7.8) with EDTA (0.1 mM) demonstrated the highest specific activity. PAGE results indicated that bitter orange peel contains five isoenzymes of MnSOD and one isoenzyme of CuZnSOD. Melon peel contains two isoenzymes of both MnSOD and FeSOD and one isoenzyme of CuZnSOD. Watermelon peel contains two isoenzymes of CuZnSOD and one isoenzyme each of FeSOD and MnSOD.

Conclusions: The Ananas melon variety demonstrated the highest SOD activity and specific activity among various local melon varieties. This makes its peels an exceptionally efficient source for extracting an enzyme with numerous pharmaceutical and cosmeceutical applications.